U.S. patent number 10,136,507 [Application Number 15/582,978] was granted by the patent office on 2018-11-20 for silicon based ion emitter assembly.
This patent grant is currently assigned to Illinois Tool Works Inc.. The grantee listed for this patent is Illinois Tool Works Inc.. Invention is credited to Peter Gefter, Aleksey Klochkov.
United States Patent |
10,136,507 |
Gefter , et al. |
November 20, 2018 |
Silicon based ion emitter assembly
Abstract
An embodiment of the invention provides a method for low
emission charge neutralization, comprising: generating a high
frequency alternating current (AC) voltage; transmitting the high
frequency AC voltage to at least one non-metallic emitter; wherein
the at least one non-metallic emitter comprises at least 70%
silicon by weight and less than 99.99% silicon by weight; wherein
the at least one emitter comprises at least one treated surface
section with a destroyed oxidation layer; and generating ions from
the at least one non-metallic emitter in response to the high
frequency AC voltage. Another embodiment of the invention provides
an apparatus for low emission charge neutralization wherein the
apparatus can perform the above-described operations.
Inventors: |
Gefter; Peter (South San
Francisco, CA), Klochkov; Aleksey (San Francisco, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Illinois Tool Works Inc. |
Glenview |
IL |
US |
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Assignee: |
Illinois Tool Works Inc.
(Glenview, IL)
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Family
ID: |
54192448 |
Appl.
No.: |
15/582,978 |
Filed: |
May 1, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170238404 A1 |
Aug 17, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15178448 |
Jun 9, 2016 |
9642232 |
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14665994 |
Jun 28, 2016 |
9380689 |
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12456526 |
Jun 18, 2009 |
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61132422 |
Jun 18, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B
9/041 (20130101); B32B 27/32 (20130101); B32B
7/12 (20130101); B32B 15/08 (20130101); B32B
15/085 (20130101); H05F 3/04 (20130101); H01T
23/00 (20130101); B32B 17/10174 (20130101); B08B
7/0035 (20130101); B32B 15/082 (20130101); B32B
17/10009 (20130101); B32B 27/302 (20130101); H05F
3/06 (20130101); H01T 19/04 (20130101); B32B
15/18 (20130101); H01L 31/048 (20130101); B32B
2307/712 (20130101); B32B 2307/202 (20130101); Y02E
10/50 (20130101); B32B 2457/12 (20130101); Y10T
428/24942 (20150115); B32B 2255/205 (20130101); B32B
2270/00 (20130101); B32B 2307/73 (20130101); B32B
2307/7265 (20130101); B32B 2255/06 (20130101); B32B
2307/554 (20130101); B32B 2255/20 (20130101); B32B
2307/412 (20130101); B32B 2307/306 (20130101); B32B
2307/558 (20130101) |
Current International
Class: |
H05F
3/04 (20060101); H01T 19/04 (20060101); B32B
9/04 (20060101); H01T 23/00 (20060101); B08B
7/00 (20060101) |
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Primary Examiner: Leja; Ronald W
Assistant Examiner: Clark; Christopher
Attorney, Agent or Firm: McAndrews, Held & Malloy,
Ltd.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a Continuation of and claims priority to U.S.
patent application Ser. No. 15/178,448, filed Jun. 9, 2016, which
is a Continuation of and claims priority to U.S. patent application
Ser. No. 14/665,994, filed Mar. 23, 2015, which is a
Continuation-In-Part of and claims priority to U.S. patent
application Ser. No. 12/456,526, filed Jun. 18, 2009, entitled
"SILICON EMITTERS FOR IONIZERS WITH HIGH FREQUENCY WAVEFORMS" which
claims the benefit of and priority to U.S. Provisional Application
No. 61/132,422, filed Jun. 18, 2008. U.S. patent application Ser.
No. 15/178,448, U.S. patent application Ser. No. 14/665,994, U.S.
patent application Ser. No. 12/456,626 and U.S. Provisional Patent
Application Ser. No. 61/132,422 are both hereby incorporated herein
by reference.
Claims
What is claimed is:
1. An apparatus, comprising: a silicon based ion emitter configured
with a tip, a taper, a shaft, and a tail; wherein the taper is
between the tip and the shaft; wherein the shaft is between the
taper and the tail; wherein the emitter comprises a treated surface
on at least one of the shaft or the tail, the treated surface
having a higher electrical conductivity or a lower resistivity than
the taper and the tip; wherein the emitter comprises an assembly of
a non-metallic portion and a metallic portion; wherein the metallic
portion is constructed as a compressing spring sleeve positioned on
the shaft of the emitter; wherein the assembly comprises a first
ratio S/D in a range from approximately 0.03 to 0.06; wherein S is
a thickness of the sleeve that receives the emitter; and wherein D
is a diameter of the shaft of the emitter.
2. The apparatus as defined in claim 1, wherein the emitter
comprises a second ratio L/S in the range (2-5)/[tan {tangent}
(0.5.alpha.)]; wherein L is a length of an exposed portion of the
shaft of the emitter; wherein .alpha. is an angle of a taper of a
tapered portion of the shaft of the emitter.
3. The apparatus as defined in claim 1, wherein the tip of the
emitter generates ions in response to a contact of the treated
surface of the emitter to an alternating current (AC) having a
frequency range of 1 kilohertz to 100 kilohertz.
4. The apparatus as defined in claim 1, wherein the treated surface
of the emitter comprises an area with a roughness in a range of 0.5
micron to 10 microns.
5. The apparatus as defined in claim 1, wherein the treated surface
of the emitter comprises a metallic plating or metallic
coating.
6. The apparatus as defined in claim 1, wherein the emitter
comprises more than 72.00% silicon by weight and less than 99.99%
silicon by weight.
7. An apparatus, comprising: a silicon based ion emitter configured
with a tip, a taper, a shaft, and a tail; wherein the taper is
between the tip and the shaft; wherein the shaft is between the
taper and the tail; wherein the emitter comprises a treated surface
on at least one of the shaft or the tail, the treated surface
having a higher electrical conductivity or a lower resistivity than
the taper and the tip; wherein the emitter comprises a second ratio
L/S in a range (2-5)/[tan {tangent} (0.5.alpha.)]; wherein L is a
length of an exposed portion of the shaft of the emitter; wherein S
is a thickness of a sleeve that receives the emitter; wherein
.alpha. is an angle of a taper of a tapered portion of the shaft of
the emitter.
8. The apparatus as defined in claim 7, wherein the emitter
comprises more than 72.00% silicon by weight and less than 99.99%
silicon by weight.
9. The apparatus as defined in claim 7, wherein the tip of the
emitter generates ions in response to a contact of the treated
surface of the emitter to an alternating current (AC) having a
frequency range of 1 kilohertz to 100 kilohertz.
10. The apparatus as defined in claim 7, wherein the treated
surface of the emitter comprises an area with a roughness in a
range of 0.5 micron to 10 microns.
11. The apparatus as defined in claim 7, wherein the treated
surface of the emitter comprises a metallic plating or metallic
coating.
12. A ionizing bar, comprising: a high voltage generator; and a
silicon based ion emitter coupled to the high voltage generator and
configured to generate positive ions and negative ions, the emitter
configured with a tip, a taper, a shaft, and a tail; wherein the
taper is between the tip and the shaft; wherein the shaft is
between the taper and the tail; wherein the emitter comprises a
treated surface on at least one of the shaft or the tail, the
treated surface having a higher electrical conductivity or a lower
resistivity than the taper and the tip; wherein the emitter
comprises an assembly of a non-metallic portion and a metallic
portion; wherein the metallic portion is constructed as a
compressing spring sleeve positioned on the shaft of the emitter;
wherein the assembly comprises a first ratio S/D in a range from
approximately 0.03 to 0.06; wherein S is a thickness of the sleeve
that receives the emitter; and wherein D is a diameter of the shaft
of the emitter.
13. The ionizing bar as defined in claim 12, further comprising a
socket into which the emitter is connected to receive a high
voltage signal from the high voltage generator.
14. The ionizing bar as defined in claim 13, wherein the high
voltage generator is configured to provide at least a corona onset
voltage to the emitter via the sleeve and the socket.
15. The ionizing bar as defined in claim 12, wherein the emitter is
coupled to the high voltage generator via the sleeve and a metallic
pin.
16. The ionizing bar as defined in claim 12, wherein the emitter
comprises a second ratio L/S in the range (2-5)/[tan {tangent}
(0.5.alpha.)]; wherein L is a length of an exposed portion of the
shaft of the emitter; wherein .alpha. is an angle of a taper of a
tapered portion of the shaft of the emitter.
17. The ionizing bar as defined in claim 12, wherein the high
voltage generator is configured to provide an alternating current
(AC) in a high frequency range of 1 kilohertz to 100 kilohertz and
sufficiently high voltages to cause the emitter to emit positive
and negative ions.
18. The ionizing bar as defined in claim 12, further comprising a
measuring device for monitoring a surface or/and volume electrical
resistance and composition of the emitter.
19. The ionizing bar as defined in claim 12, wherein the treated
surface of the emitter comprises a metallic plating or metallic
coating.
20. The ionizing bar as defined in claim 12, wherein the emitter
comprises more than 72.00% silicon by weight and less than 99.99%
silicon by weight.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments of the invention primarily relate to ionizing devices
that are used for static charge neutralization and control. More
specifically, embodiments of the invention are targeted at the need
for reliable and low particle emission ionizers within the
semiconductor, electronics, and/or flat panel industries.
With AC ionizers, each emitter receives a high positive voltage
during one time period and a high negative voltage during another
time period. Hence, each emitter generates corona discharge with
output of both positive and negative ions.
A stream (cloud) of positive and negative ions is directed toward a
charged target(s) for the purpose of neutralizing the charges and
preventing static charge associated technological problems.
2. Description of Related Art
The background description provided herein is for the purpose of
generally presenting the context of the present disclosure. Work of
the presently named inventors, to the extent the work is described
in this background section, as well as aspects of the description
that may not otherwise qualify as prior art at the time of filing,
are neither expressly nor impliedly admitted as prior art against
this present disclosure.
Ion emitters of charge neutralizers generate and supply both
positive ions and negative ions into the surrounding air or gas
media. To generate gas ions, the amplitude of the applied voltage
must be high enough to produce a corona discharge between at least
two electrodes arranged as an ionization cell. In the ionization
cell, at least one electrode is an ion emitter and another one may
be a reference electrode. Also it is possible that the ionization
cell includes at least two ionizing electrodes.
Along with useful positive gas ions and negative gas ions, emitters
of charge neutralizers may create and emit corona byproducts
including unwanted particles. In a semiconductor process and
similar clean processes, particle emission/contamination correlate
with defects, product reliability problems, and lost of
profits.
Several known in the art factors influence the quantity of unwanted
particles emission. Some of primer factors include, for example,
the material composition, geometry, and design of the ion emitter.
The second one includes the arrangement of the emitter connection
to a high voltage power supply. Another critical factor is
associated with a profile of electrical power (magnitude and time
dependence of high voltage and current) that is applied to the ion
emitters.
The power waveforms can be used to control the voltage profile that
is applied to the emitters by the high voltage power supplies.
Voltage/current waveforms can be used to control both ion
generation and particle emission by emitter(s).
Corona discharge can be energized by DC (direct current) voltage,
AC (alternating current) voltage, or a combination of both
voltages. For many applications of this invention, a preferable
power waveform is a high frequency high voltage (HF-HV) output from
a high frequency (HF) power supply, as will be discussed below.
This high voltage output may be continual rather than continuous.
That is, the voltage output may be variable by amplitude in time or
turned off periodically.
The material composition of emitters is known to affect particle
emission levels of ionizers. Common emitter materials include
stainless steel, tungsten, titanium, silicon oxide, single crystal
silicon, silicon carbide, and other nickel or gold plated metals.
This list is not complete. From the experience of the inventors,
metallic type emitters are prone to generate more particles as a
result of corona associated erosion and spattering. Moreover,
metallic or, in general, highly conductive particles are often
considered as "killer particles" in the semiconductor industry
(i.e., the particles are able to short-circuit tightly positioned
conductive traces of wafers/chips). So, in the frame of this patent
application the inventors basically consider non-metallic ion
emitters, as will be discussed below.
In one of these materials, a super clean (more than 99.99% plus
purity) single crystal silicon is suggested by Scott Gehlke in U.S.
Pat. No. 5,447,763 from the viewpoint of low particle emission.
This single crystal silicon has been adopted by the semiconductor
industry as a de-facto clean emitter standard. A super clean
silicon carbide (at least 99.99% pure) suggested by Curtis et al.
in U.S. patent application publication No. 2006/0071599 is another
non-metallic material. However, silicon carbide emitters are
expensive and prone for emission of undesirable particles.
Known ionizers with single crystal silicon emitters are powered by
two high voltage DC supplies. A system, like the room ionization
system "NiLstat" 5000 (Ion Systems, Inc.) for cleanroom ceiling
installation, typically produces less than 60 particles per cubic
foot of air that are greater than 10 nanometer (diameter). Other
emitter materials typically produce more than 200 particles per
cubic foot of air that are greater than 10 nanometer (diameter).
Some materials produce thousands of particles per cubic foot of air
that are greater than 10 nanometer (diameter).
Although some of (1) components of emitter materials, (2) elements
of connector construction for a non-metallic emitter, and (3)
application of special power waveforms may be known to be
independently important, the prior art has not considered the
benefits of strategically combining these factors to reach high
ionization reliability and cleanliness.
Recent experiments by the inventors have resulted in the inventors
discovering and finding novel combinations that lead to stable ion
production and unpredictably low levels of particle generation by
the emitter. Clean and/or low particle emission ionizers have
utility in several high technology industries. In particular, the
semiconductor industry has a well-defined need for super clean
ionizers. The ionizers are needed to minimize static charges and
electrical fields, which can destroy semiconductor devices. As low
as possible particle emission is also required because foreign
particles may compromise the reliability of semiconductor devices.
Leading edge semiconductor technology is building 24-16 nanometer
features on wafers. For the nanometer features, control of
particles greater than 10 nanometers is absolutely needed.
It is to be understood that both the foregoing general description
in the background section are exemplary and explanatory only and
are not restrictive of the invention, as claimed.
BRIEF SUMMARY OF THE INVENTION
Recent experiments by the inventors have shown that (1) the
composition of silicon based material and emitter design, (2) the
arrangement and/or construction of the emitter connector, and (3)
the type of power voltage waveforms should be considered as a
complex novel beneficial combination for reliable performance of
and low particle emission by the emitter. Found combinations by the
inventors lead to stable ion production and unpredictably low
levels of particle generation by the emitter. Clean and/or low
particle emission ionizers have utility in several high technology
industries. In particular, the semiconductor industry has a
well-defined need for super clean ionizers. The ionizers are needed
to minimize static charges and electrical fields, which can destroy
semiconductor devices. As low as possible particle emission is also
required because foreign particles may compromise the reliability
of semiconductor devices. Leading edge semiconductor technology is
building 24-16 nanometer features on wafers. For the nanometer
features, control of particles greater than 10 nanometers is
absolutely needed.
Matching of the emitter electrode composition comprising silicon
based material, electrode connector, and power waveform that is
applied to the emitter have proven to be a novel method of
achieving previously unattainable levels reliability and
cleanliness of a charge neutralizing ionizer. The core of exemplary
embodiments of this invention is the combination of the following:
non-metallic ion emitter having material/chemical composition in
the range between less than 99.99% to at least 70% silicon by
weight, emitter electrode design and surface treatment
(preparation), connection arrangement for the emitter, and
operating in a high frequency range high voltage power supply. In
this combination the high frequency high voltage power generates
mode of corona discharge featured by low onset voltages. The ions
generated from at least one non-metallic emitter in an embodiment
of the invention comprises positive ions and negative ions that are
generated at minimum onset HF voltage and power.
This combination is effective and applicable for many different
types of clean room ionizers/charge neutralizers. As an example, an
ionizer in an embodiment of the invention can be considered an
in-line ionizer targeted for a class 1 cleanroom production
environment. This ionizer may have an incoming flow of clean dry
air (CDA) or nitrogen, argon, or other noble gas. The gas or air
passes along the silicon based emitter inside an ionizing cell. The
ionizing cell/chamber is typically enclosed except for the air/gas
inlet and outlet openings.
The design of an in-line charge neutralizing ionizer according to
embodiments of the invention can be using a compact power source
like high frequency high voltage supply. An output connector of the
power supply accommodates at least one silicon based emitter. An
ionization cell produces clean bipolar ionization. The air stream
(or nitrogen or argon stream or other gas stream) suffices to move
the ions from the ionizing emitter (cell or chamber) to a target of
charge neutralization.
The high frequency voltage profile of the power supply has an AC
frequency range of approximately 1 KHz to 100 kHz. Peak voltages
exceed the corona onset voltages (positive and negative) of the
emitters. An ion current of the emitter at high frequency AC is
substantially limited by the electrical resistance of the silicon
based material.
Within this instant application, high voltages are defined as the
difference in potentials between at least one ion generating
electrode and the reference electrode. In some high frequency AC
ionizing cells the reference electrode can be isolated from the
ionizing electrode by dielectric wall. Therefore, possibilities of
direct electrons, ions avalanches (like spark discharge) between
electrodes are practically excluded and particle emission from the
emitter is greatly diminished. During operation mode ions are
generated whenever the voltage amplitude exceeds the corona
positive and negative onset voltages applied to the ionizing
electrode.
Another frequency (optional) becomes pertinent when the high
frequency AC voltage profile is periodic rather than continuous.
That is, the high frequency AC voltage exceeding the onset voltage
profile is generated only within predefined time intervals. In this
scenario, the high frequency AC voltage is applied to the emitters
during active time intervals (typically approximately 0.01 second
or less to approximately 1 or more seconds), but a lower than onset
voltage can be applied during inactive time intervals. This
optional high frequency voltage waveform may also include
essentially an on/off high voltage mode. A normal low voltage or
on/off frequency range is approximately 0.1 Hertz to 500 Hertz, but
the frequency may lie outside this range.
Some silicon-containing emitter compositions are provided as
examples. They are: (a) doped crystal silicon, (b) doped poly
silicon, (c) combination doped silicon and silicon oxide, and (d)
deposited on substrate doped silicon. Dopants and additives are
mainly targeted to control surface and volume electrical
resistivity, as well as the mechanical property of silicon based
emitters. They preferably are taken from known non-metallic dopant
groups like boron, arsenic, carbon, phosphorous, and others.
Accordingly, at least one exemplary embodiment of the invention
provides a method for low emission charge neutralization,
comprising: generating a high frequency alternating current (AC)
voltage; transmitting the high frequency AC voltage to at least one
non-metallic emitter; wherein the at least one emitter comprises at
least 70% silicon by weight and less than 99.99% silicon by weight;
wherein the at least one non-metallic emitter comprises at least
one treated surface section with a destroyed oxidation layer; and
generating ions from the at least one non-metallic emitter in
response to the high frequency AC voltage.
At least one exemplary embodiment of the invention also provides an
apparatus comprising elements that permit the above-described
functionalities. For example, an embodiment of the invention
provides an apparatus for low emission charge neutralization,
comprising: at least one non-metallic emitter comprising at least
70% silicon by weight and less than 99.99% silicon by weight;
wherein the at least one non-metallic emitter comprises at least
one treated surface section with a destroyed silicon oxide layer;
and wherein the at least one non-metallic emitter generates ions in
response to the high frequency AC voltage.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory only and are not restrictive of the invention, as
claimed.
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate one (several)
embodiment(s) of the invention and together with the description,
serve to explain the principles of the invention.
BRIEF SUMMARY OF THE FIGURES
Non-limiting and non-exhaustive embodiments of the invention are
described with reference to the following figures, wherein like
reference numerals refer to like parts throughout the various views
unless otherwise specified.
It is to be noted, however, that the appended drawings illustrate
only typical embodiments of this invention and are therefore not to
be considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
FIG. 1(a) is an illustration of a conventional single crystal
silicon ion emitter, or (in general) a non-metallic ion
emitter.
FIGS. 1(b) and 1(c) show illustrations of conventional parts and an
assembly of a single crystal silicon emitter with metal sleeves and
grooves.
FIG. 2 shows an illustration of a conventional DC room ionization
ceiling system with two single crystal silicon emitters.
FIG. 3(a) shows an illustration of a silicon-containing emitter,
according to an embodiment of the invention, wherein the emitter
comprises a section of the emitter shaft having a preselected
surface roughness (or a treated surface section).
FIG. 3(b) shows an illustration of an emitter, according to another
embodiment of the invention, wherein the emitter comprises a
section of the emitter shaft having a partial conductive surface
plating or partial conductive surface coating (or treated surface
section of other types).
FIG. 3(c) shows an illustration of a silicon-containing emitter and
an apparatus to monitor the surface electrical resistance and/or
volume electrical resistance of the emitter, in accordance with an
embodiment of the invention.
FIGS. 4(a) and 4(b) show illustrations of a silicon-containing
emitter with two variants of radial compression spring sleeves and
metal pins, in accordance with various embodiments of the
invention.
FIGS. 5(a), 5(b), and 5(c) show illustrations of three
silicon-containing emitters that have different configurations of
the taper and tip, in accordance with various embodiments of the
invention.
FIG. 6 shows an illustration of an HF waveform to perform "soft"
plasma cleaning of a silicon-containing emitter tip during "start
up" of corona ionization period, in accordance with an embodiment
of the invention.
FIGS. 7(a), 7(b), and 7(c) show illustrations of examples of high
frequency power voltage wave forms applied to a silicon based
emitter during an operational mode, in accordance with various
embodiments of the invention.
FIGS. 8(a) and 8(b) show illustrations of examples of modulated
high frequency voltage wave forms, in accordance with various
embodiments of the invention.
FIG. 9(a) shows an illustration of an ionizing cell/chamber of an
in-line ionizer, in accordance with an embodiment of the invention.
A high frequency AC powered silicon based emitter generates both
polarity ions. An air/gas flow is moving the stream of ions from
the emitter.
FIG. 9(b) shows an illustration of the gas channel and the
ionization cell, in accordance with an embodiment of the
invention.
FIG. 9(c) shows a simplified block diagram of an in-line ionizer
with a silicon based emitter, in accordance with an embodiment of
the invention.
FIGS. 10(a), 10(b), 10(c), and 10(d) show illustrations of a
simplified structure of a high frequency AC ionizing bar, and
details of nozzles with silicon based ion emitters, in accordance
with an embodiment of the invention.
DETAILED DESCRIPTION
In the following detailed description, for purposes of explanation,
numerous specific details are set forth to provide a thorough
understanding of the various embodiments of the present invention.
Those of ordinary skill in the art will realize that these various
embodiments of the present invention are illustrative only and are
not intended to be limiting in any way. Other embodiments of the
present invention will readily suggest themselves to such skilled
persons having the benefit of this disclosure.
In addition, for clarity purposes, not all of the routine features
of the embodiments described herein are shown or described. One of
ordinary skill in the art would readily appreciate that in the
development of any such actual implementation, numerous
implementation-specific decisions may be required to achieve
specific design objectives. These design objectives will vary from
one implementation to another and from one developer to another.
Moreover, it will be appreciated that such a development effort
might be complex and time-consuming, but would nevertheless be a
routine engineering undertaking for those of ordinary skill in the
art having the benefit of this disclosure. The various embodiments
disclosed herein are not intended to limit the scope and spirit of
the herein disclosure.
Exemplary embodiments for carrying out the principles of the
present invention are described herein with reference to the
drawings. However, the present invention is not limited to the
specifically described and illustrated embodiments. A person
skilled in the art will appreciate that many other embodiments are
possible without deviating from the basic concept of the invention.
Therefore, the principles of the present invention extend to any
work that falls within the scope of the appended claims.
As used herein, the terms "a" and "an" herein do not denote a
limitation of quantity, but rather denote the presence of at least
one of the referenced items.
Experimentally, it has been shown by the inventors that, for
example, an in-line ionizer combining (1) silicon-containing
emitter (2) configured as a pin type electrode in contact with a
conductive socket and capacitive receiving (3) a high frequency AC
voltage waveform reliably produces an electrically balanced ion gas
stream with very few particles. The above-noted combination creates
ionization with reliability and cleanliness levels that cannot be
reached separately by either known in the art non-metallic
silicon-containing emitters or the high frequency AC voltage
waveform. Cumulative particles greater than or equal to 10 nm in
diameter were measured during cleanliness testing. The particle
counters (like CNC--condense particle counter) did not separate
particles into size ranges.
For example, two single crystal silicon emitters for a clean room
ionization system (e.g., NiLstat ionization system) (similar to the
system 200 shown in FIG. 2) connected to a DC or pulsed DC (+/-20
kV) power source (discussed in U.S. Pat. No. 5,447,763) generate
roughly 60 particles (greater than 10 nanometers in diameter) per
cubic foot of air. In contrast, an ionizer disclosed by an
embodiment of the invention typically yields less than 10
same-diameters of nano-particles per cubic foot of air. In
perspective, 10 particles per cubic foot of air greater than 10
nanometers is nominally 6 times cleaner than the cleanest prior art
ionizers at the time of this application.
In a contrasting example, a metallic emitter (tungsten) was tested
with a conventional system (e.g., the system in U.S. Pat. No.
5,447,763) and showed an unacceptable in clean room amount of
particle emission. Our experiment to use a tungsten emitter in
combination with a high frequency AC high voltage waveform similar
to that suggested in U.S. patent application publication No.
2003/0007307 (to Lee et al.) had little benefit in cleanliness
compared to that conventional system that was previously disclosed
in U.S. Pat. No. 5,447,763. The particle concentration count
results in both cases of testing tungsten emitters were above 600
particles (greater than 10 nanometers) per cubic foot of air.
However, a high purity (99.99% plus purity) single crystal silicon
emitter (like the emitter shown in FIGS. 1(a), 1(b), and 1(c)) has
high electrical resistance (in the mega Ohms range). When this
emitter(s) is connected to a high frequency (HF) AC voltage power
source often ion production is not enough for efficient charge
neutralization. The main reason is because most of the HF (high
frequency) electrical current/voltage goes to a stray capacitor but
not to the emitter tip.
Another problem associated with a high purity (99.99% plus purity)
single crystal silicon emitter is that the emitter is prone to
create a surface oxide "skin" (oxide layer or skin shown by dashed
line 102c that surrounds the surface of the silicon emitter 101c in
FIG. 1(c)). This skin/layer 102c is composed of a highly isolative
silicon oxide (SiO.sub.2). Silicon oxide growth on the surface of a
clean silicon wafer is discussed, for example, in the following
publication by Stanford University, California, "Growth of native
oxide" Stanford University Nanofabrication Facility, 28 Aug.
2003.
An end result of the silicon oxide layer growth phenomenon is that
a non-metallic silicon emitter/pin is surrounded by this isolative
layer and does not have good, reliable connection with an
electrical socket and hence to a high voltage output of an HF power
supply.
Another non-metallic ion emitter is discussed in U.S. patent
application publication No. US 2006/0071599 to Curtis et al. This
emitter is made from high purity 99.99% silicon carbide. This
material is a composite with about 30% carbon. It is known in the
art that silicon carbide has high hardness. Silicon carbide is also
expensive in machining to produce as a pin type emitter
configuration. Also, silicon carbide has a metallic type high
electrical conductance. Conductive particles from a composite with
high carbon content are often undesirable in the semiconductor
industry.
Wide acceptance of silicon material in the semiconductor industry
dictates relatively low cost of the ion emitter material. Moreover,
mechanical properties of silicon-based material made machining
simple (cutting, polishing, and so on). A small concentration of
silicon dopants and additives are mainly targeted to control the
surface and volume electrical resistivity, as well as to improve
mechanical property of silicon based emitters. They preferably can
be taken from known non-metallic dopant groups like boron, arsenic,
carbon, phosphorous, and others.
Silicon based composition with silicon content which is less than
99.99% and more than 70% by weight made possible to reach
electrical resistance of emitters in the kilo-ohms range, in an
embodiment of the invention. This resistance is low enough to
conduct high frequency current and to support stable corona
discharge. So, the two following certain factors consistently
interact to create the observed cleanliness improvement: the
composition and design of silicon based emitter and the high
frequency AC emitter driving power/voltage waveform.
One of the advantages of the combination of silicon based emitters
and HF voltage waveform is that the onset voltage of corona
discharge is significantly lower (approximately 1,000 V to 3,000 V
or more) than for DC, pulse DC, or low frequency (50 Hz to 60 Hz)
voltages for non metallic emitters.
A possible explanation of this effect is that at high frequency in
the range (approximately 1 kHz to 100 kHz or more), the voltage
applied to the emitter changes polarity in the milliseconds range
or micro seconds range. That is why corona charge carriers
(positive and negative ions, electrons) do not have enough time to
move far away from the emitter tip. Also, specific surface charge
conservation (often named as "charge memory") properties of silicon
based material may play a role in electrode surface electron
emission. That is why both positive and negative high frequency
corona onset voltages are low. With lower voltage of HF corona
discharge, the particle emission from the silicon based emitter is
also low.
The scientific basis for the particle emission improvement in
corona discharge of balanced ionizers due to the interaction
between non-metallic silicon based emitter and the high frequency
AC voltage waveform is currently being studied. Recognized theories
of corona discharge and/or of ionization and/or of particle
emission from non-metallic emitters do not predict or completely
explain the experimental cleanliness observed.
However, how to make and use the instant invention is clearly
understood. The following written description is directed toward
explaining how to make and use this invention to one of ordinary
skill in the static charge control field.
Experimental works directed to embodiments of the invention
comprising a combination of silicon based emitter's composition and
HF voltage waveform showed that, in some instances, ionizers with
brand new or long time idle emitters show a problem to start HF
corona discharge and reliably produce ion generation. Measurements
show high contact resistance between the silicon emitters and
electrical sockets. This high resistance is one of the reasons for
the corona start problem of the ionizing device. Process formation
of a relatively thick (in 10.sup.th to 100.sup.th or more
Angstroms) oxide "skin" on silicon wafers in open air are recorded
in the above-cited reference, "Growth of native oxide" Stanford
University Nanofabrication Facility. For example, during six days,
the SiO.sub.2 surface layer can reach thickness of 12 Angstrom.
Silicon oxide is known as a good insulator. So, this skin growth
results in a higher surface and contact resistance of the silicon
based emitters. The rate of oxide layer growth is variable and
dependent from many ambient atmospheric factors like oxygen and
ozone concentration (see, "Silicon oxidation by ozone" at the web
link
http://iopscience.iop.org/0953-8984/21/18/183001/pdf/cm9_18_183001.pdf),
temperature, moisture, and so on. Ozone is one of the byproducts of
corona discharge and may accelerate oxidation of a silicon emitter.
This phenomenon has a profound effect for relatively low power
voltage of HF ionizers with silicon based non-metallic emitters. An
exemplary embodiment of the invention includes surface treatment of
a silicon based emitter to decrease contact resistance between the
emitter and metallic socket.
FIG. 1(a) is an illustration of a conventional silicon emitter
100a. The emitter 100a comprises four distinctive parts: tip 101a,
taper 102a, shaft 103a, and tail 104a. The shape and size of the
tip 101a depends on the available amount of high voltage and
current from HVPS (high voltage power supply), material of the
emitter as well as technology and methods of production. The
emitter tip 101a is usually the most critical part of any ion
emitter. The emitter tip 101a is directly exposed to corona
discharge and determines the life span of the emitter. Silicon
emitters has a generally cylindrical shaft 103a. The shaft 103a
mainly defines the length of the emitter and distance between the
taper and socket or receptacle connected to the high voltage power
supply. The taper or cone 102a is a transitional part between the
tip 101a and shaft 103a. Silicon is a brittle material by nature
and the taper angle is a compromise of mechanical strength and
electrical characteristics of the emitter. Tail 104a may be
rounded, beveled, or chamfered. This part should assist in
inserting the emitter 100a into a socket or receptacle. Standard
high purity silicon emitters have a smooth surface as a result of
chemical polishing (which is usually achieved by strong acid
treatment).
FIG. 1(b) shows an illustration of a silicon emitter with a
metallic sleeve. The silicon emitter 100a comprises a non-metallic
silicon part 101b and stainless steel tube 102b (or sleeve 102b)
with a dimple 105b. The sleeve 102b should protect the brittle
silicon emitter 101a from mechanical (handling) damage. The sleeve
102b also should improve electrical connection of a non-metallic
high purity silicon emitter and metallic sockets or receptacles.
Views 103b and 104b show the assembled drawings of a silicon
emitter 100a with metallic sleeve 102b. View 106b presents a cross
section of the assembled emitter shaft 103a.
A big part (or a significant portion) of the silicon shaft 103a is
encased into metal sleeve 102b as it is shown in view 103b. To fix
the sleeve 102b on the silicon shaft 103a and achieve reliable
electrical contact between them it is common to make at least one
protrusion 105b (dimple) on the sleeve 102b. Taking into
consideration the tolerances in dimensions of all three components
(diameter of silicon emitter shaft, inner diameter of the sleeve
and depth of the dimple) the assembly operation is quite
challenging (see cross sectional view silicon shaft and dimple on
view 106b).
FIG. 1(c) shows an illustration of another design of a silicon
emitter 100c. The emitter part 101c is shown with a surface
oxidation layer ("skin") 102c presented by a dashed line. The
emitter 100c comprises a silicon part 101c and sleeve 103c with
dimple 104c. Sleeve 103c may have one or more sections/extension
parts 106c with grooves 107c. The emitter assembly is shown in view
105c. This design permits to keep the emitter in nozzles and uses
extension parts 106c for inserting extension parts 106c into
different sockets or receptacles.
FIG. 2 shows an illustration of a conventional DC room ionization
system 200 similar to that used in U.S. Pat. No. 5,447,763. The
ionizer has a couple of rods, positive (+) rod 201 and negative rod
(-) 202, carrying single crystal silicon emitters. The rods are
connected to dedicated positive and negative high voltage power
(HVDC) supplies 203 (placed in a chasse). Cross sectional view of
the emitter rod is shown in view 204. The end part of the rod 202
has a socket type connector 205 and a high voltage cable 206
connected to the HV DC power supplies 203. The socket 205
accommodates a silicon type emitter 207 shown in view 204. Other
parts of the rod 202 serve as protectors of the emitter 207,
connector 205 and HV cable 206 from a destructive force. The rod
design makes the silicon emitters 201, 202 to be exchangeable.
At least some goals of exemplary embodiments of the invention are
to suggest low particle emission, by economical silicon based
charge neutralization systems. A composition of a silicon based
emitter which has less than 99.99% and more than 70% silicon by
weight in combination with high frequency corona discharge make the
goal of low particle emission achievable. For a non-metallic
silicon electrode in the ionization system, the next primary goal
is to provide a reliable electrical connection between the silicon
based emitter and HF high voltage power supply.
FIG. 3(a) shows an illustration of a silicon based emitter 300a
according to an embodiment of the invention, wherein the emitter
300a comprises an abrasive portion or sand casting treated portion
310a (i.e., treated surface section 310a) of shaft 301a which can
be inserted in a high voltage socket (not shown). This portion 310a
of the shaft surface 302a has roughness H in the range of
approximately 0.5 micron to 10 micron (see view 303a). During
surface treatment, for example by sanding, the oxide "skin"
previously on the shaft surface 302a will be destroyed and deleted
or otherwise removed. Sanding creates an emitter shaft surface
profile which is able make multi-spot contacts with the high
voltage socket (not shown). Optionally, similar surface treatment
can be applied to the rounded end 304a of the tail 314a of the
emitter 300a. The emitter tip 305a, taper 306a, and part 311a of
the shaft 301a has regular chemically polished surfaces.
One more embodiment of a silicon based emitter is illustrated in
FIG. 3(b). According to this embodiment of the invention, the
silicon based emitter 300b comprises a portion 310b (i.e., treated
surface section 310b) of the emitter shaft 301b having a metallic
plating or metallic coating 302b (or conductive plating or metallic
coating 302b) which makes the portion 310b of the shaft 301b to be
a good surface conductor and protect contact portion 316 of emitter
300b from oxidation in the long term. The contact portion 316 can
be in the tail 314b of the emitter shaft 301b.
Different known methods of silicon plating (e.g., like vacuum
deposition, electrolytic plating, spraying, and others) can be
used. Plating materials like metals may include: e.g., nickel,
brass, silver, gold, and other metals as well as alloys acceptable
in semiconductor industry.
FIG. 3(c) shows an illustration of a silicon-containing emitter and
an apparatus to monitor the surface electrical resistance and/or
volume electrical resistance of the silicon-containing emitter, in
accordance with an embodiment of the invention. This shows an
example of an electrical quality control operation of silicon based
emitters 300c as shown in FIG. 3(c). The control and/or monitoring
include electrical resistance measurements or monitoring the
electrical resistance and/or composition of the emitter 300c or a
treated surface section 302c of the emitter 300c. Conductive
electrodes 303c and 304c are attached to or connected to the sanded
parts 302c (or treated surface section 302c) of emitter shaft 301c
and tail 314c, respectively, of the emitter 300c. Standard
resistance R measuring device 305 can be used to make and record
measurements of the electrical resistance R. This way, complex
surface and volume resistivity and the emitter composition can be
monitored. The required normal quality and composition (with less
than 99.99% to at least 70% silicon by weight) silicon based
emitters should have complex resistance in kilo ohms range. After
surface treatment and control operation the emitter 300c can be
inserted into a standard metallic socket (not shown) to minimize
formation of new layers of silicon oxide "skin".
At least some of the exemplary embodiments shown herein allow
solving of two fold problems: (1) creating reliable electrical
connection between non-metallic silicon based emitters and sockets;
and (2) protecting the contacting portion of the emitter from
oxidation.
FIGS. 4(a) and 4(b) show illustrations of a silicon-containing
emitter with two variants of radial compression spring sleeves and
metal pins, in accordance with various embodiments of the
invention. The silicon-containing emitter and metal pin are
inserted into the sleeve, as discussed below. The silicon based
emitter 400a of FIG. 4(a) in an embodiment of the invention will
first be described. According to this exemplary embodiment, the
emitter 400a comprises the emitter part 401a wherein the silicon
portion of the emitter part 401a has a reduced length/shaft
diameter ratio. The short silicon based emitter part 401a is
connected to a metal radial compression spring sleeve 402a from one
side 430 of the sleeve 402a. The other side 431 of the sleeve 402a
is connected to a solid metal extension pin 403a. The metal pins
403a and 403b discussed herein can be metal electrodes 403a and
403b that are inserted into spring type sleeves 402a and 402b,
respectively. This pin 403a may have at least one (or more) groove
and a variable length "L2" required by the socket and an ionization
cell (including reference electrode) design. For example, the pin
403a includes grooves 435 and 436, although the pin 403a may only
have a single groove in other embodiments. The pin 403a can be, for
example, a solid metal pin or tube. Conventional, CNC, or automatic
metal cutting machines, or other metal proceeding methods can be
used to manufacture a pin 403a. View 405a shows an illustration or
drawing of the emitter assembly 410a with the silicon emitter 400a
according this exemplary embodiment. Radial compression spring
sleeve 402a has significantly bigger contact area with silicon part
401a compared with the conventional sleeve 102b with the dimple
105b as shown in FIGS. 1(a) and 1 (b). The result is more reliable
electrical connection and less mechanical stress applied to a
brittle silicon emitter part 401a. The design of silicon emitter
with metal sleeve has some requirements to prevent "secondary"
corona discharge from an edge of the sleeve to a nearby reference
electrode. Main parameters which should be taken into consideration
are illustrated in view 406a: D which is a diameter of the silicon
emitter shaft 440; L which is a length of exposed portion 441 of
the silicon emitter shaft 440; a which is an angle of the taper of
tapered portion 442 of the shaft 440; and S which is the thickness
of the sleeve 402a. For a high concentration electrical field on
the emitter tip 421a of silicon part 401a (or on the emitter tip
421b of silicon part 401b), the first ratio S/D should be in the
range of approximately 0.03 to 0.06. Another requirement related to
the distance between the emitter tip 421a and sleeve 402 is the
second ratio L/S:the ratio L/S should be in the range (2-5)/tan
{tangent} (0.5.alpha.). The parameter a is an angle of a taper of a
tapered portion of the shaft 440 of the at least one non-metallic
emitter part 401a or 401b. These conditions of a new silicon
emitter design in one embodiment of the invention will satisfy
several criteria/specifications: reliable electrical connection,
good mechanical strength, and minimum possibility of "secondary"
corona will generate particles emission from metal parts.
FIG. 4(b) shows an illustration of another embodiment of a silicon
based emitter 400b comprising another configuration of a metal
radial compression spring sleeve 402b. In this case, the emitter
400 comprises a silicon emitter part 401b has a diameter D1 and one
end 461 of metal sleeve 402b has a diameter D3. Silicon emitter
part 401b has an emitter tip 421b. Part 403b is a solid metal pin
403b which has diameter D4 and another end 462 of the sleeve 402b
has a diameter D2. Differences in diameters (D1>D3) of silicon
emitter part 401b and metal sleeve 402b create a required
compression force to provide a reliable or good electrical contact
between the silicon part 401b and metal sleeve 402b. Similarly,
differences in diameters (D2<D4) provide a reliable or good
electrical connection between metal sleeve 402b and metal pin 403b.
Views 404b and 406b show assembled views of the silicon emitter
400b. View 405b is a cross sectional view which shows, according to
this exemplary embodiment, the silicon emitter 401b and sleeve
sections 402b having big contact areas with minimum contact
pressure and local stress. The assembly operation is simplified.
Both exemplary embodiments (emitters 400a and 400b) use a minimum
amount of expensive silicon based material, have big reliable
contact areas of non-metallic emitter shaft with metal sleeves, and
good dimensional matching to standard sockets or receptacles.
In some cases silicon based emitters have problem to start high
frequency corona discharge and reliably produce ion generation in
spite of having normal surface/volume electrical resistance and
good electrical connection to high voltage sockets. Our experiments
show that the core of this problem is due to the formation of thick
isolative oxide "skin" on the surface of the emitter tip ("working
horse" of the emitter). One more exemplary embodiment of this
invention addresses this problem. The shape of the tip of the
silicon-containing emitters may have some positive effect on the
rate of formation and thickness of isolative oxide "skin".
FIGS. 5(a), 5(b), and 5(c) show illustrations of three
silicon-containing emitters that have different configurations of
the taper and tip, in accordance with various embodiments of the
invention. The various tip configurations and taper configurations
shown in FIGS. 5(a), 5(b), and 5(c) determine an operating HF
corona onset voltage and ionization current parameters.
In FIG. 5(a), there is shown a silicon based emitter 501 with a
flattened truncated tip. This tip design is prone to create a ring
type high frequency corona discharge (where flattened tip 510 meets
the taper 511 of the emitter 501). This emitter 501 may reduce ion
current density and particle emission. However, it is characterized
by higher onset HF corona voltage. The taper 511 is at an angle
value of .alpha. with respect to the flattened tip 510.
Silicon based emitter 502 (FIG. 5(b)) has small rounded tip 514
with a radius Z in the range of approximately 60 microns to 400
microns which is less expensive in production and minimizes corona
current fluctuation. The taper portion 516 (of emitter 502) extends
from the small rounded tip 514.
A sharpened silicon based emitter 503 (FIG. 5(c)) has a sharp
pointed tip 520 with a radius Y in the range of approximately 40
microns to 50 microns, or less. This emitter 503 has the lowest
corona onset voltage V.sub.on. However, the ion current density for
the emitter 503 is at maximum and spattering, erosion, and oxide
"skin" growths are at the highest rate. This silicon based emitter
503 preferably used for ionization in oxygen free gases like
nitrogen or argon. The taper/conical portion 521 of the emitter 503
preferably has angle .alpha. in the range of approximately 10
degrees-20 degrees with respect to the sharp pointed tip 520. All
silicon based emitters (501, 502, 503) have a composition according
to exemplary embodiments of this invention and are able to provide
low particle counts when installed in in-line ionizers, ionizing
bars, and other charge neutralizers driven by the HF AC voltages.
The degree of sharpness and the curvature of the tip (i.e.,
configuration of the tip) affect or determine ionizer operating
parameters including onset voltage, ion current, and ion balance,
but they do not affect the scope of the instant invention.
One more exemplary embodiment of this invention addresses oxide
"skin" growth on the silicon emitter tip. The embodiment uses
specific mode of corona discharge to clean the silicon emitter tip
from the oxide skin and help ionizer start up independently from
the emitter profile.
FIG. 6 shows an illustration of an HF waveform to perform "soft"
plasma cleaning of a silicon-containing emitter tip during a "start
up" of a corona ionization period, in accordance with an embodiment
of the invention.
The high voltage "HF startup" type waveform 600 is applied to the
emitter. This mode of high voltage drive provides a group (numbered
from 1 to up to several hundred bipolar pulses 605) of short
duration bipolar voltage bursts to the emitter during the start-up
period (marked as a Ts period). Thanks to the very short duration
of power profile in the range milliseconds, microseconds or less,
the HF corona associated plasma has very limited energy. This way
prevents both a rising temperature of the emitter tip and a surface
destruction (spattering, erosion, and particle emission) of the
emitter tip. Short duration HF plasma bursts performs only "soft"
cleaning of the emitter tip from silicon oxide skin. The duration
of the "startup" time period Ts, burst pulse amplitude, and the
number of pulses may vary and depend from thickness of the silicon
oxide skin, gas media, emitter tip design, and so on. The voltage
amplitude of HF burst pulses is significantly higher (approximately
25% to 100% or more) than normal (operational) corona onset
voltages positive (+)Von and negative (-)Von (shown in FIG. 6 by
two dash horizontal lines 610 and 615, respectively). The initial
"startup" mode helped to start normal/operational high frequency
corona discharge and ion production. During normal/operational mode
(during time Top), the high voltage amplitude can be only 10%-20%
higher than corona onset voltages (+)Von or (-)Von to minimize
particle emission. In continuous operation mode the HF corona
discharge is able to protect silicon emitter from oxidation in
clean dry gas media. Therefore, soft plasma cleaning of the at
least one non-metallic emitter is performed during a start up
period of a corona ionization period by a voltage/power waveform
different from a voltage/power waveform during an operational
period.
FIGS. 7(a), 7(b), and 7(c) show illustrations of examples of high
frequency power voltage wave forms applied to a silicon based
emitter during an operational mode, in accordance with an
embodiment of the invention. The different operational HF voltage
waveforms effectively create bipolar ionization for silicon based
emitters. The function of the high frequency AC voltage is to
create both polarity ions (positive ions and negative ions) at a
minimum driving voltage. To create ions, the peak voltages
(positive and negative peak voltages) exceed the corona onset
voltages. As shown in FIG. 7(a), the high frequency AC voltage
profile 700 is continuous, but the profile may also be modulated
continuous or non-continuous and periodic.
FIG. 7(a) presents a continuous sign wave type powering voltage 700
which may have a frequency range from approximately 1 kHz up to
approximately 100 kHz. Positive and negative voltage amplitudes of
the voltage 700 are higher than positive corona onset voltage
(+)Von 705 and lower than the negative corona onset voltage (-)Von
710. This voltage type waveform 700 provides maximum power to the
silicon based emitter described herein and create maximum ion
current.
FIG. 7(b) shows an illustration of a voltage waveform 750
comprising groups of pulse trains 752 with "on" periods 755 and
"off" periods 756. The waveform 750 comprises at least one
modulation portion, wherein each modulation portion comprises a
pulse train 752 having an on period 755 and an off period 756.
During an on period 755 in a pulse train 752, the waveform 750 has
an amplitude 758 that exceeds the positive corona onset voltage
threshold 705 and that exceeds the negative corona onset voltage
threshold 710 for a particular emitter. During an off period 756 in
a pulse train 752, the waveform 750 has an amplitude 760 that does
not exceed the corona onset voltage thresholds 705 and 710. In the
example of FIG. 7(b), this amplitude 760 is a voltage magnitude of
approximately zero. Additional details of the waveforms 700, 750,
and 780 in FIGS. 7(a), 7(b), and 7(c), respectively, are also
described in commonly-owned and commonly-assigned U.S. Pat. No.
8,009,405 to Peter Gefter et al. During "off" periods 756 (which
can be small duty factor), corona discharge (ion production) and
particle emission stops. The duty factor can be variable in the
range from approximately 100% down to approximately 0.1% or less
depending upon a required ion output. A minimal duty factor helps
to suppress particle emission and emitter erosion rate.
FIG. 7(c) shows an illustration of another variant of voltage
waveform 780 where a duty factor is close to approximately 100%,
but the voltage amplitude applied to the silicon emitter
periodically drops to values lower than the corona onset voltage
(in the range of approximately 90% to approximately 50% or less
from corona onset voltage). An advantage of this waveform is that
it may minimize both particle emission and high voltage swing
(voltage/electrical field variation).
The waveform 780 comprises at least one modulation portion, wherein
each modulation portion comprises a pulse train 782 having an on
period 785 and a non-operation period 786. During an on period 785
in a pulse train 782, the waveform 780 has an amplitude 788 that
exceeds the positive corona onset voltage threshold ((+)Vmax) 705
and that exceeds the negative corona onset voltage threshold
((-)Vmax) 710 for a particular emitter. During a non-operation
period 786 in a pulse train 782, the waveform 780 has an amplitude
790 that does not exceed the corona onset voltage thresholds 705
and 710, but the amplitude 790 is more than zero volts.
FIGS. 8(a) and 8(b) show illustrations of examples of modulated
high frequency voltage wave forms, in accordance with an embodiment
of the invention. FIG. 8(a) presents a continuous modulated
waveform 800 as a result of mixing (combination) of high frequency
and low frequency voltages. The low frequency component (or offset
voltage) is shown in FIG. 8(b). This voltage waveform 850
predominately creates ions by a high frequency component (similar
to the waveform 700 shown in FIG. 7(a)) and moves ions from the
emitter by the low frequency component.
In-line ionizers with silicon based emitters can be used in the
most critical operations/processes (e.g., environments like
Airborne Particulate Cleanness Class 1) in the semiconductor
industry. FIGS. 9(a), 9(b), and 9(c) present illustrations of
simplified views of ionization cells and block diagrams of the
in-line ionizer. With an in-line ionizer design, the application of
the HF frequency voltage may be similar to the waveform shown in
FIG. 8(a) with extended in range from approximately 20 kHz to
upward of approximately 100 kHz.
FIG. 9(a) shows an illustration of an ionizing cell/chamber of an
in-line ionizer, in accordance with an embodiment of the invention.
A high frequency AC powered silicon based emitter 902a generates
both polarity ions. An air/gas flow 908a is moving the stream of
ions from the emitter 902a. Also shown in FIG. 9(a) an ionization
cell 900a is connected to HF HV generator 901a. Silicon based
emitter 902a is positioned in a socket 903a and is connected via
capacitor (C1) which is connected to the HF generator 901a. The
emitter 902a may have sanded or metal plated portion of the shaft
as previously discussed in FIG. 3(a) and FIG. 3(b), respectively,
to provide reliable connection to socket 903a.
The emitter 901a is typically positioned in the middle part of
air/gas channel 904a. Preferably, the reference electrode 905a
positioned on an outer side of the channel 904a and close to the
outlet 906a of channel 904a. The reference electrode 905a is
connected to control system 907a. Positive ions 920 and negative
ions 921 are generated by the emitter 901a when the peak voltages
(positive or negative voltages) of the high frequency AC voltage
(applied to emitter 901a) exceed the corona onset voltage. Air/gas
flow 908a from an external source (not shown) still need to move a
generated ion cloud toward distant target charge neutralization
(not shown). Corona discharge near the tip 909a of the emitter 902a
creates intense HF plasma 910a with ions and electrons near the tip
909a of silicon emitter 902a. The corona onset voltage is
approximately (+) 5 to 6 kV for positive ions and (-) 4.5 to 5.5 kV
for negative ions.
Generation/emission corona byproducts like particles in plasma are
minimized by methods, apparatuses, and means previously discussed
as the combination of ion emitter composition, ion emitter design,
and powered voltage waveforms.
FIG. 9(b) shows an illustration of another view 900b of the
ionization cell and gas channel in a block 901b, in accordance with
an embodiment of the invention. The channel 902b has an inlet 933b
and an outlet 934b. The silicon based emitter 905b with socket 906b
can be made as an exchangeable unit positioned in a cavity 960 of
the channel 902b. The emitter socket 906b and reference electrode
907b are connected to high voltage HF power supply 908b. Ionized
gas flow (shown by arrows 961) are moving ion clouds to the charged
target 909b like wafer and the ion clouds will neutralize these
charges 965 on the charged target 909b.
FIG. 9(c) shows a simplified block diagram of an in-line ionizer
900c with a silicon based emitter 904c, in accordance with an
embodiment of the invention. Positive and negative ions 901c are
created inside the ionization cell 902c. A high voltage HV-HF power
supply 903c provides the voltage and current needed to generate the
ions 901c. The power supply 903c delivers a high frequency AC
voltage to the silicon based emitter 904c through capacitor C1.
Voltage on the silicon based emitter 904c is relative to a
reference electrode 905c.
A pressurized source of air, nitrogen, or argon is connected to the
in-line ionizer 900c via an inlet to create an air flow or gas flow
906c. The air flow or gas flow 906c entrains positive and negative
ions 901c and carries the ions 901c through the ionizer outlet 934c
toward a target (e.g., target 909b in FIG. 9(b)).
The in-line ionizer 900c includes a control system 907c comprising
a microprocessor 908c, gas pressure sensor 909c, corona discharge
sensor 910c, and operation status indicators 911c. The in-line
ionizers 900c are often working in semiconductor tools having
wafers load/unload operations. That is why the in-line ionizers
900c may have a relatively long idle ("stand off") periods without
corona discharge and gas flow. During those time periods the tip of
silicon emitter may grow silicon oxide layer. As previously
discussed in an exemplary embodiment illustrated in FIG. 3(a) and
FIG. 6, the control system 907c initiates gas ionization process by
starting the high voltage power supply 903c in the "startup" mode.
The corona discharge sensor 905c and processor 908c are
continuously monitoring the status of corona discharge up to the
point when a strong and stable corona and ion production are
achieved. After that, the control system 907c and power supply 903c
are switched to the normal operation mode.
FIGS. 10(a), 10(b), 10(c), and 10(d) show illustrations of a
simplified structure of a high frequency AC ionizing bar 1000a, and
details of nozzles with silicon based ion emitters, in accordance
with an embodiment of the invention. FIGS. 10(a) and 10(b) shows
views of a high frequency AC ionizing bar 1000a with a plurality of
raw silicon based emitters 1001a through 1008a (as an example).
Each silicon emitter has a stainless steel sleeve. The stainless
steel sleeve is shown as sleeve 1020c in FIG. 10(c), and as sleeve
1020d in FIG. 10(d). Each stainless steel sleeve 1020a is installed
in a nozzle. Each nozzle has socket and optionally one or two
air/gas jet orifices. Cross sectional view of the nozzles are shown
as nozzles 1030c in FIGS. 10(c) and 1030(d) in FIG. 10(d).
The socket 1009c is connected to a common high voltage bus and the
orifices to manifold (not shown) both located inside enclosure
1010a of the ionizer bar 1000a. The cross-sectional view 1040 of
the nozzle 1030d shows the relative position of the silicon emitter
1003d (with sleeve and groove as previously discussed in FIGS. 4(a)
and 4(b)) and orifices 1004d. The bus distributes HF power from the
high voltage AC power supply to each nozzle and emitter. The HF-HV
power supply with microprocessor based control system is preferably
position inside the same enclosure 1010a. The silicon based ion
emitters receive HF AC voltages in the range of approximately 6 kV
to 8 kV with basic frequency at approximately 10 kHz to 26 kHz
(similar to shown in FIG. 7(a)). This HF high voltage creates
corona discharge between each emitter 1001a through 1008a and
reference electrode 1011a. This high frequency AC voltage is
sufficient in itself to create a clean bipolar ionization when the
composition of the emitter is in the range from less 99% to with
greater than 70% silicon are employed. As previously discussed the
high frequency itself is not able to move ion cloud far away. HF
ionizing bars 1000a often installed in flat panel or semiconductor
tools at relatively short distance (e.g., approximately 50 mm to
300 mm) from targets. The electrical field of charged target (not
shown) attracts ions opposite polarity in this case. However, for
efficient charge neutralization at longer distances (e.g.,
approximately 400 mm to 1500 mm) ions cloud requires assistance
from an air/gas flow or an electrical field, or combination of
both. Often HF ionizing bars can be used in combination with HEPA
filters providing clean laminar air flow.
FIG. 8a shows modulated HF waveform 800 which creates an additional
low frequency field (with a frequency of approximately 0.1 Hz to
200 Hz) to help ion delivery to the target. During periods T2 the
amplitude 802 of positive voltage wave 804 and amplitude 806
negative voltage wave 808 are almost equal, and so the offset
voltage is close to zero and ion clouds oscillate near silicon
emitters. In contrast, during periods like T1 the voltage waveform
800 has a positive offset 810 and positive polarity ion clouds
(which are repelled) are moving to the target (see FIG. 8(b)).
Similarly, during time periods like T3 voltage waveform 800 has a
negative offset 815 and negative polarity ion clouds (which are
repelled) are moving to the target. The amplitude and frequency of
offset voltages depends from distance between ionizing bar 1000a
and target.
High frequency ionizing bars 1000a with silicon based emitters are
able to create low emission, to create clean air/gas ionization,
and to neutralize charges of fast moving large objects (like flat
panels) at distances of, for example, approximately 400 mm up to
1500 mm.
Another embodiment of the invention provides a method for low
emission charge neutralization, wherein the at least one
above-described non-metallic emitter comprises a reduced silicon
section length/shaft diameter ratio.
Another embodiment of the invention provides a method for low
emission charge neutralization, wherein the above-described sleeve
comprises a metal radial compression spring sleeve and wherein
differences in diameters of the at least one emitter, metal pin,
and sleeve create a compression force that provide a reliable
electrical connection between the at least one emitter, sleeve, and
metal electrode.
Another embodiment of the invention provides an apparatus for low
emission charge neutralization, wherein the at least one
above-described non-metallic emitter comprises a reduced
length/shaft diameter ratio.
Another embodiment of the invention provides an apparatus for low
emission charge neutralization, wherein the above-described sleeve
comprises a metal radial compression spring sleeve and wherein
differences in diameters of the at least one emitter, metal pin,
and sleeve create a compression force that provide a reliable
electrical connection between the at least one emitter, sleeve, and
metal electrode.
Another embodiment of the invention provides an apparatus for and
method of creating reliable, low-particle emission charge
neutralizers by combining: non-metallic ion emitters having
chemical composition in the range between less than 99.99% to at
least 70% silicon by weight, emitter geometry, and surface
treatment (preparation), and a connection arrangement between the
emitter and a high voltage power supply operating in high frequency
range. In this combination the emitter reliably generates the high
frequency corona discharge featured by low onset voltage and low
particle emission. This combination is effective for many different
type clean room ionizers/charge neutralizers targeted for clean
rooms of class 1. The combination of silicon-containing emitters
and a high frequency AC voltage produces ionizers that are cleaner
than conventional ionizers, based on particles counts greater than
10 nanometers. This improvement in cleanliness has been
experimentally determined by the inventors.
The above description of illustrated embodiments of the invention,
including what is described in the Abstract, is not intended to be
exhaustive or to limit the invention to the precise forms
disclosed. While specific embodiments of, and examples for, the
invention are described herein for illustrative purposes, various
equivalent modifications are possible within the scope of the
invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the
above detailed description. The terms used in the following claims
should not be construed to limit the invention to the specific
embodiments disclosed in the specification and the claims. Rather,
the scope of the invention is to be determined entirely by the
following claims, which are to be construed in accordance with
established doctrines of claim interpretation.
* * * * *
References